Fluid boxes and full screen recording

Thank you for your response.  That is interesting about the simulation being recorded using the blank master slide and the blank master slide being the only one without fluid boxes.  Thank you for that and it looks as though there isn't an easy solution to my request.  

The end result I want to achieve is to be able to record a simulation using full screen.  At the moment, I can do that and save it as a responsive course.  However, when I preview it, and change the screen size to see what it would look like on different size screens, it either shows only part of the screen or squashes it depending on the selection in the Properties bar.  I would like to see the whole screen keep to scale as I reduce the screen size.  This can be achieved using a Fluid Box.  I can create a number of slides with a fluid box in each of them and cut and paste the background into the fluid box, but I was wondering if there was a quicker way to do it.  I know it's not ideal for elearning but it's what the customer wants.